Oh don’t get me wrong, our intrepid adventurers are going to have to spend a good chunk of time on this with no guarantee they live long enough.

However assuming knowledge isn’t a gap (given they already built a time machine), iron ore is fairly abundant in many areas of the world, and it’s relatively straightforward to build a kiln that would reach the appropriate temperatures to smelt the iron into bloom (that can be hammered into workable iron)

It’ll take many, many years, but assuming they can avoid ending up as food, it doesn’t seem impossible